1. Field of the Invention
The present invention relates to a surface emitting laser element, a surface emitting laser array, an optical scanning unit, an image forming apparatus and a method of manufacturing a surface emitting laser element; and in more detail, to a surface emitting laser element and a surface emitting laser array in which laser light is emitted in a direction perpendicular to a surface of a substrate, an optical scanning unit having the surface emitting laser element or the surface emitting laser array, an image forming apparatus having the optical scanning unit, and a method of manufacturing a surface emitting laser element in which laser light is emitted in a direction perpendicular to a surface of a substrate.
2. Description of the Related Art
A vertical cavity surface emitting laser is such that light is emitted in a direction perpendicular to a surface of a substrate, and recently has drawn attention because of low cost, low power consumption, small size, being suitable for a two-dimensional device, and high performance, in comparison to an edge-emitting-type semiconductor laser such that light is emitted in a direction parallel to a surface of a substrate (see Japanese Laid-Open Patent Application No. 2002-208755 (Patent Document 1) and Japanese Laid-Open Patent Application No. 2004-200211 (Patent Document 2), for example).
A process of manufacturing a surface emitting laser element includes a process of wiring for electrically connecting a p-side electrode and an electrode pad. In this process, because the p-side electrode is formed on the top of a mesa, wiring across a large step is carried out, and thus, may cause a disconnection or a degradation in reliability of the wiring because of an insufficiency of a step coverage of a wiring member. The step coverage means a state of the wiring member covering the step.
Therefore, an improvement of the step coverage of the wiring member as a result of the mesa having a taper shape (see Japanese Laid-Open Patent Application No. 09-33949 (Patent Document 3), Japanese Laid-Open Patent Application No. 2006-013366 (Patent Document 4) and Japanese Laid-Open Patent Application No. 2007-150170 (Patent Document 5), for example), covering the entirety of a side wall of the mesa with the p-side electrode material (see Japanese Laid-Open Patent Application No. 2008-34637 (Patent Document 6), for example), increasing the wiring width on the side wall of the mesa (see Japanese Laid-Open Patent Application No. 2009-302113 (Patent Document 7)), and so forth, have been proposed. Further, Japanese Laid-Open Patent Application No. 2009-94332 (Patent Document 8) discloses a surface-emitting-type semiconductor laser device in which a taper is formed on a metal wiring that is formed on the top of the mesa, and further, the taper is covered by an interlayer dielectric film.
However, in a liquid crystal display device disclosed in Patent Document 3, the taper for the step is formed to have multiple stages, and an etching condition of wet etching or dry etching may be changed each time the taper angle for the step changes. Therefore, an in-plane distribution of the etching shape becomes a distribution of the shape of the step, thus uniformity of the shape of the step may not be satisfactory, and it may be difficult to manufacture the liquid crystal display device with a high yield.
Further, in a surface emitting semiconductor laser disclosed in Patent Document 4, the mesa has the taper shape and the wiring is formed. In this configuration, because an angle of a peripheral part of the top end of the mesa is close to a right angle, the wiring may be disconnected at this part, and thus, it may be difficult to manufacture the surface emitting semiconductor laser with a high yield.
Further, in a semiconductor laser disclosed in Patent Document 5, wiring is formed after the mesa is formed to be the taper shape through wet etching. In this configuration, because an angle of a peripheral part of the top end of the mesa is close to a right angle, the wiring may be disconnected at this part, and thus, it may be difficult to manufacture the surface emitting semiconductor laser with a high yield.
Further, Patent Document 6 discloses an example of a surface emitting semiconductor laser in which the entire surface of the side wall of the mesa is covered by metal wiring. In this configuration, variation in laser characteristics may be caused by stress in the metal wiring, which may result in a reduction of yield.
Further, in a surface emitting laser disclosed in Patent Document 7, the mesa has the taper shape and wiring is formed. In this configuration, because an angle of a peripheral part of the top end of the mesa is close to a right angle, the wiring may be disconnected at this part, and thus, it may be difficult to manufacture the surface emitting semiconductor laser with a high yield.
Further, in a surface emitting semiconductor laser disclosed in Patent Document 8, as shown in FIG. 15, at a top part of a mesa 5100, an end part of a contact metal 5101 having a taper shape is formed at a position away from the top end of the mesa 5100 by the distance “X”. Further, an interlayer dielectric film 5102 is formed on an area (“X”) at which a part of the top end of the mesa 5100 is exposed. Further, metal wiring 5103 is formed. In this surface emitting semiconductor laser, a part at which a thickness of the wiring material is very small (L4) may exist at an area indicated as “PART HAVING RISK OF DISCONNECTION”. Therefore, it may be difficult to manufacture the surface emitting semiconductor laser with a high yield.